Study of the Action of Reciprocating Parts. Important Help from Mr.
Frederick J. Slade. Paper before Institution of Mechanical Engineers.
Appreciation of Zerah Colburn. The Steam Fire Engine in England.
After the close of the Paris Exposition I devoted myself in earnest
to the study of the action of the reciprocating parts of the engine,
and will here give a sketch of its development. In the high-speed
steam-engine the reciprocating parts were found to be a most essential
feature. Besides transmitting the pressure of the steam to the crank
they perform quite another office. It is their inertia, relieving the
crank from shocks on the dead centers, and equalizing the distribution
of the pressure on it through the stroke, that makes the high-speed
engine possible. I employed this inertia before I knew anything
about it. I had been occupied with the subject of balancing. I had
demonstrated practically that the centrifugal force of a weight equal
to that of the reciprocating parts, opposite the crank and at the
same distance from the center as the crank-pin, perfectly balanced
a horizontal engine, and had shown this fact conclusively at this
exposition.
The problem before me was, “What is it that makes my engine run so
smoothly?” I am not a mathematician, and so could not use his methods.
I got along by graphic methods and study of the motion of the piston
controlled by the crank. My recollection of the several steps of my
progress is quite indistinct. One thing I do remember distinctly, and
that is the help that I got from my friend Frederick J. Slade, who
was younger than I, but who died several years ago. Mr. Slade was a
mathematical genius. The firm of Cooper, Hewitt & Co. were at a later
date the pioneer makers in the United States of wrought-iron beams
and other structural shapes; and all their designs and computations
were the work of Mr. Slade. I had formed his acquaintance in London
in ’63. I met him again in Paris in ’67. He was then in France in the
employ of Abram S. Hewitt, investigating the Siemens-Martin process
of steel manufacture. He took much interest in the engine. One day he
brought to me a diagram representing the two now famous triangles, and
a demonstration of them which he had made, showing that the ordinates,
representing the acceleration or retardation of the piston motion at
every point, if erected on the center line of the engine, terminate in
a diagonal line, which, with a connecting-rod of infinite length, would
cross this center line at its middle point.
This exhibited at once the equalizing action of the reciprocating parts
in a cut-off engine, absorbing the excessive force of the steam at the
commencement and imparting it to the crank at the end of the stroke. I
feel myself more indebted to Mr. Slade than to any one else, and would
here record the tribute of my grateful acknowledgment.
On January 30, 1868, I had the honor of reading a paper on the Allen
engine before the Institution of Mechanical Engineers. The discussion
of the paper was postponed until the next meeting, April 30, and the
paper was ordered meantime to be printed and sent to the members.
The result was that on the latter date we had a very interesting
discussion. I may mention two things which occurred at the first
meeting, but do not appear in the report of the transactions. When the
secretary reached the statement that the acceleration of the piston
was greatest at the commencement of the stroke, the president of
the meeting, Sampson Lloyd, Esq., one of the vice-presidents of the
Institution, stopped the reading and said to me, “You do not mean,
Mr. Porter, that this is _on_ the commencement of the stroke, but at
a point near its commencement.” I was obliged to answer him that I
intended to say that precisely on the dead center, at the point where
motion in one direction had ceased and that in the opposite direction
had not yet commenced, at that precise point the stress on the crank
was at its maximum, the crank having brought the reciprocating parts
to rest, and then by a continuance of the same effort putting them in
motion in the reverse direction.
[Illustration: FREDERICK J. SLADE]
After the reading was concluded, Mr. E. A. Cowper took the floor,
and stated that I was entirely mistaken in my explanation of this
action, that this had been investigated by a gentleman whose name he
gave but which I have forgotten, and who had demonstrated that this
retarding and accelerating action was represented by a curve, which
approximately he drew on the blackboard, but which he excused himself
from demonstrating there, as it would require the use of the calculus
and would take considerable time. For this reason the discussion
was postponed. At the next meeting Mr. Cowper did not present this
demonstration, and long afterwards he wrote a letter to the editors
of _Engineering_, stating that on full investigation he had found
the retardation and acceleration of the piston to be represented by
triangles and not by a curve. At the discussion of the paper my view
was supported by all the speakers who addressed themselves to this
point, except Mr. Cowper. An especially careful and valuable exposition
of the action of the reciprocating parts was given Mr. Edwin Reynolds,
then of the Don Steel Works, Sheffield.
Zerah Colburn, the editor of _Engineering_, had always taken a
warm interest in my engine, and in the winter following the Paris
Exposition he invited me to furnish him the drawings and material for
its description in his paper. This I did, and from these he prepared
a series of articles written in his usual clear and trenchant style.
These will be found in Volume V of _Engineering_, the cuts following
page 92, and the articles on pages 119, 143, 158, 184, and 200.
Mr. Colburn’s articles in _Engineering_ are so interesting in
themselves that I think I need make no apology for quoting from them
his remarks on this subject of the inertia of the reciprocating
parts, and those in which is depicted the revolutionary nature of the
high-speed engine, as viewed at that time.
After a prelude, with most of which the reader is already acquainted,
Mr. Colburn says:
“When a steam-engine is brought from abroad to the very spot where the
steam-engine originated, and where it has received, so far at least as
numbers are concerned, its greatest development, and is claimed to be
superior to those produced here, and to be able to run advantageously
at a speed hitherto deemed impracticable, its promoters must not
expect to have much attention paid to its claims until such attention
has been actually compelled, and then they must be prepared for an
ordeal of severest criticism....
“In employing a high grade of expansion, especially with the
considerable pressure of steam now usually carried in stationary
boilers, two serious practical difficulties are met with. The first
arises from the injurious effect of the sudden application of so great
a force on the centers, which the beam-engine, indeed, cannot be made
to endure, and the second is found in the extreme difference between
the pressures at the opposite ends of the stroke, which is such that
the crank, instead of being acted upon by a tolerably uniform force, is
rotated by a succession of violent punches, and these applied when it
is in its most unfavorable position....
“In the Allen engine the action of high speed causes all the practical
difficulties which lie in the way of the successful employment of high
grades of expansion combined with high pressure of steam completely
to disappear. The crank receives as little pressure on the centers as
we please; none at all if we like; the force is applied to it as it
advances, in a manner more gradual than the advocates of graduated
openings and late admission ever dreamed of, and a fair approximation
is made to a uniform rotative force through the stroke. So that, in a
properly constructed engine, the higher the speed the smoother and more
uniform and more silent the running will be.”
After a page or more devoted to a demonstration of this action,
Mr. Colburn sums up the advantage of high speed in the following
illustration:
“Let us suppose that, in an engine making 75 revolutions per minute,
the reciprocating parts are of such a weight that the force required
at the commencement of the stroke to put them in motion is equal to
a pressure of 20 pounds on the square inch of piston. This will not
modify the diagram of pressure sufficiently to produce much practical
effect. But let the number of revolutions be increased to 150 per
minute, the centrifugal force of these parts as the crank passes the
centers is now equal to 80 pounds on the square inch of piston, and any
pressure of steam below this amount acts only as a relieving force,
taking the strain of these parts partly off from the crank. It makes no
matter how suddenly it is admitted to the cylinder, not an ounce can
reach the crank; but as the latter advances, and the acceleration of
the reciprocating parts becomes less, the excess of force not required
to produce this becomes, in the most gradual manner, effective on the
crank.
“It will be observed how completely the designer has this action of
the reciprocating parts under control. He can proportion their speed
and weight to the pressure of steam in such a manner as to relieve the
crank from the blow on the center to whatever extent he may wish. The
notion that the reciprocating parts of high-speed engines should be
very light is therefore entirely wrong. They should be as heavy as they
can be made, and the heavier the better.
“The advantages of more rapid rotation are largely felt in the
transmission of power. Engineers understand very well that,
theoretically, the prime mover should overrun the resistance. Motion
should be not multiplied but reduced in transmission. This can seldom
be attained in practice, but high speed gives the great advantage of
an approximation to this theoretical excellence. On the other hand,
slow-speed engines work against every disadvantage. Coupled engines and
enormous fly-wheels have to be employed to give a tolerably uniform
motion; often great irregularities are endured, or the abominable
expedient is resorted to of placing the fly-wheel on the second-motion
shaft. Then comes the task of getting up the speed, with the ponderous
gearing and the enormous strains. Slow motion also prevents the use of
the belt, immeasurably the preferable means of communicating power from
a prime mover.
“But how about the wear and tear? The question comes from friends and
foes alike. The only difference is in the expression of countenance,
sympathetic or triumphant. The thought of high speed brings before
every eye visions of hot and torn bearings, cylinders and pistons cut
up, thumps and breakdowns, and engines shaking themselves to pieces. It
is really difficult to understand how so much ignorance and prejudice
on this subject can exist in this day of general intelligence. The fact
is, high speed is the great searcher and revealer of everything that is
bad in design and construction. The injurious effect of all unbalanced
action, of all overhanging strains, of all weakness of parts, of all
untruth in form or construction, of all insufficiency of surface,
increases as the square of the speed. Put an engine to speed and its
faults bristle all over. The shaking drum cries, ‘Balance me, balance
me!’ the writhing shaft and quivering frame cry, ‘See how weak we are!’
the blazing bearing screams, ‘Make me round!’ and the maker says, ‘Ah,
sir, you see high speed will never do!’
“Now, nothing is more certain than that we can make engines, and that
with all ease, in which there shall be _no_ unbalanced action, _no_
overhanging strains, _no_ weakness of parts, _no_ untruth of form
or construction, _no_ insufficiency of surface; in which, in short,
there shall be _no_ defect to increase as the square of the speed, and
then we may employ whatever speed we like. ‘But that,’ interposes a
friend, ‘requires perfection, which you know is unattainable.’ No, we
reply, nothing unattainable, nothing even difficult, is required, but
only freedom from palpable defects, which, if we only confess their
existence, and are disposed to get rid of, may be easily avoided. It
is necessary to throw all conceit about our own work to the dogs, to
lay down the axiom that whatever goes wrong, it is not high speed,
but ourselves who are to blame, and to go to high speed as to our
schoolmaster.
“Among the many objections to high speed, we are often told that the
beam-engine will not bear it, and the beam-engine, sir, was designed
by Watt. In reverence for that great name, we yield to no one. The
beam-engine, in its adaptation to the conditions under which it was
designed to work--namely, a piston speed of 220 feet per minute and a
pressure of one or two atmospheres--was as nearly perfect as any work
of human skill ever was or will be; but we wonder why the outraged
ghost does not haunt the men who cling to the material form they have
inherited, when the conditions which it was designed to meet have been
all outgrown, who have used up his factor of safety, and now stand
among their trembling and breaking structures, deprecating everything
which these will not endure.
“A journal and its bearings ought not only never to become warm, but
never even to wear, and, if properly made, never will do so with
ordinary care to any appreciable extent, no matter how great speed is
employed. It is well known that there exists a very wide difference in
bearings in this respect, some outlasting dozens of others. Now, there
need be no mystery about this: the conditions of perfect action are
so few and simple that it seems almost idle to state them. The first
is rigidity of a shaft or spindle between its bearings; but everybody
knows that if this is flexible, just in the degree in which it springs,
the journals must be cast in their bearings, though in actual practice
this perfect rigidity is not once in a thousand times even approximated
to. The point of excellence in the celebrated Sellers bearing for
shafting is that it turns universally to accommodate itself to this
flexure of the shaft, and the result is a durability almost perfect.
“The second requirement, when we have a shaft capable of maintaining
perfect rigidity under all the strains it may be subjected to, is
abundant extent of bearing surface both in length and circumference,
a requirement, it will be seen, entirely consistent with the first.
It is a mistake to use journals of small diameter with the idea that
their enlargement will occasion loss of power on account of the
increased surface velocity, as, in fact, the coefficient of friction
will diminish in a greater ratio than that in which the velocity is
increased. In the Allen engine it is intended to make all shafts and
journals too large.
“But all is of little use unless the journal is round. High speed under
heavy pressure has a peculiar way of making it known when a journal is
not round, which, we suppose, is one of its faults. Now the difference
between a true cylindrical form and such an approximation to it as a
good lathe will produce in turning ordinarily homogeneous metal is
simply amazing; but when we compare with this the forms of journals as
commonly finished, the wonder is how many of them run at all at any
speed. When ground with a traversing wheel in dead centers, which have
themselves been ground to true cones, the only known method by which
a parallel cylindrical form can be produced, their inequalities stand
disclosed, and these are usually found to be greater, often many times
greater, than the thickness of the film of oil that can be maintained
in running. Then under pressure this film is readily broken, the metal
surfaces come into contact and abrasion begins. But a true cylindrical
journal swims in an oil-bath, separated from its bearing at every
point by a film of oil of uniform thickness, and sustaining a uniform
pressure, which cannot be anywhere broken, and which has very little
inclination to work out; and if it revolves without deflection and the
pressure per square inch of surface is not sufficient to press out the
lubricant, the speed is absolutely immaterial and wear is impossible,
except that due to the attrition of the oil itself, which on hardened
surfaces has no appreciable effect.”
From the illustrations contained in these articles, I copy only the
following pair of diagrams with the accompanying note.
[Illustration: Pair of Diagrams from 18×30 Allen Engine at South Tyne
Paper Mill, 108 Revolutions, Vacuum 28 Inches. Only Half Intended Load
on Engine.]
The winter of 1867-8 was devoted by me partly to watching the
dissolving view of my engineering prospects in England. It grew more
and more evident that through my difference with Mr. Whitworth all my
efforts and successes there would come to naught, as they did.
But my friend, Mr. Lee, had even worse luck than I had. It will be
some relief from the monotony of my reverses if I go back a little
and tell of a reverse that befell another man. Curiously enough, Mr.
Lee’s reverse came from the overwhelming character of his success. The
English engineers had their breath quite taken away and lost their
heads, with the result that Mr. Lee lost his position. He was ambitious
to show his steam fire-engine doing its utmost. If he had been wiser
and had realized the limit of what his judges could stand, he would
have shown about one half its capacity and all parties would have been
happy.
To understand how naturally this most unexpected dénouement came
about, we must recall what the English people had been accustomed to.
In London fires were rare and trifling. Buildings were low, built of
brick with tile roofs. Open grates afforded the means of cooking and of
warming sufficiently for their climate. Every tenant of a building who
called in the fire department was fined five pounds, which encouraged
careful habits. The apparatus itself was something quite ridiculous.
It consisted of little hand-engines, worked by about a dozen men. On
the side of a corner building occasionally one saw painted a distance
in feet and inches. This meant that by measuring this distance from
this corner out into the street and digging a little into the macadam
pavement, a connection would be found with the water-main. From this
the water was permitted to flow gently into an india-rubber saucer some
6 feet in diameter spread on the ground. Out of this saucer the engine
drew its water for a feeble little stream.
Mr. Lee’s engine, with Worthington duplex pump, was, on its completion,
exhibited before a large company of invited guests, principally
officials of the fire department and prominent engineers. The engine
maintained a vertical column of water, delivered from a much larger
nozzle than had ever before been used in England, and considerably
over 100 feet high. There was also a corresponding column of sparks
from the chimney of the steam-pump. The exhibition was made late
in the afternoon of a short winter day, and before it was over the
coming darkness showed the column of incandescent cinders to the best
advantage. The few Americans there enjoyed this miniature Vesuvius
hugely. The Englishmen were frightened out of their wits. Their
unanimous verdict was that the engine would evidently put out a fire,
half a dozen of them for that matter, but it would kindle twenty.
And this where the engine had been pushed to its utmost, and had not
kindled one fire. Easton, Amos & Sons instantly decided that they could
never sell a steam fire-engine under Mr. Lee’s management, and they
discharged him the next morning.
During the following season we had quite a steam-fire-engine
excitement. Some one, I have forgotten who, but think it was the Duke
of Sutherland, made a public offer of a thousand pounds sterling for
the best steam fire-engine, competition to be open to all the world,
the engines to be tested for six days in the park of the Crystal
Palace at Sydenham, in the month of July following. There were a
number of amusing incidents connected with that exhibition. One was
the following: The common council of New York City determined that the
city must have that prize, so they sent over engine No. 7, a favorite
engine, one of Mr. Lee’s make, and which had been three or four years
in service. A junket committee of the city fathers accompanied it. The
London Fire Department received this delegation with great enthusiasm,
and devoted itself to making them happy. They took entire charge of
their machine and exhibited it in London to admiring crowds. A few days
before the time fixed for the opening of the trial they took the engine
to Sydenham, where on the way to its station it accidentally rolled
down a hillside and was pretty well broken up. Mr. Lee being in London
was hurriedly sent for to see if it could be repaired in time for the
trial. He found that the injuries were of so serious a nature that
the repairs could not be completed in less than three weeks. So that
competitor was out of the way. Their sympathizing friends were full of
condolence, and assumed all the cost of the repairs. They also proposed
that when the engine was put in proper order they should have an
excursion down the Thames to Greenwich and have there an exhibition of
its powers. So a steamboat was chartered and a large party accompanied
the machine to Greenwich. On arrival there it was found that the two
nozzles, a large one and a smaller one for long-distance streams, which
had been taken especial charge of by the members of a fire company, had
been accidentally dropped into the Thames. The New York delegation were
glad to get their engine back to New York without further accident.
Easton, Amos & Sons also concluded that they would like that prize.
After they had taken the engine into their own hands, they found a
number of features which seemed to them to need amendment, so they
made some quite important changes. On the second day of the trial this
engine broke down and had to be withdrawn.
I have forgotten how many competitors remained in the field, but the
prize was awarded to a London firm, builders of hand fire-engines,
who had only lately taken up this new branch of manufacture. This
successful firm applied to the government for an order to supply
steam fire-engines for the protection of the public buildings. This
application was referred to Easton, Amos & Sons, the consulting
engineers of the government. This firm concluded if possible to have
this order given to themselves, and applied to Mr. Lee to recommend the
changes in his engine necessary to put it in proper working order. Mr.
Lee replied that it was only necessary to put the engine back in the
precise condition in which he left it. They finally agreed to do this,
and employed Mr. Lee to direct the work. When completed the engine was
tried in the gardens of Buckingham Palace, in competition with the
prize winner, before a large body of government officials. The Easton,
Amos & Sons engine proved its superiority on every point so completely
that the government immediately purchased it.
Some time before this, however, Mr. Lee had associated himself with a
capitalist for the manufacture of steam fire-engines in England, and
was then engaged on plans for them. His financial associate was Judge
Winter, by which title only he was known to us. He was an American, and
before the war was the proprietor of the Winter Iron Works in Georgia
(the precise location I have forgotten), the most prominent engineering
establishment in the Southern States, in which business he had become
wealthy. He will be remembered by some gray heads as having been an
exhibitor in the New York Crystal Palace in 1853. He sent to it a
steam-engine bearing the name of “The Southern Belle.” This stood in
the machinery department, close to a Corliss engine, the two being the
only engines of any size which were exhibited there. This engine was
beautifully finished, polished pretty much all over, but its working
features were of the most ordinary character. Mechanically it was
valueless.
Judge Winter was a determined opponent of secession, and on the
adoption of that ordinance by the State of Georgia, was compelled to
fly from the country. He then took up his residence in London, to which
he had transferred such portion of his wealth as he was able to convert
into money.
He took a deep interest in the new steam fire-engine, and spent part
of nearly every day in the office where Mr. Lee and Mr. Taylor, an
American engineer whom Mr. Lee had associated with himself, were
engaged on their plans.
The point of interest to myself in this story lies here. The old judge
had no sound mechanical education, but was very fertile minded. He
came almost every morning with a new idea that he wanted embodied. It
was always absurd. He generally protested vigorously against being
overruled. When he was furnishing all the money he could not see why he
should not be allowed to have _something_ to say about it. I happened
to be present in their office one morning when he got particularly
excited over their opposition. He was a stout party, and on this
occasion I had the fun of joining in the shout of laughter that greeted
him, when, after pacing the floor in silence for a few minutes, he
exclaimed, with his hand on the fabled seat of his sympathies, “I
thank my God that if there is one thing I am free from, it is pride of
opinion.”
My recollection of the above action of Easton, Amos & Sons and of Judge
Winter contributed materially to form my imagination of the predicament
in which I would certainly find myself, should I yield to Mr. Whitworth
the power to make whatever changes might occur to him in my engine.